Electric switch.



J. J. RAWLINGS & G. SWEETSER.

ELECTRIC SWITCH.

APPLICATION FILED 312.25, 1911 1,030,207, Patented June 18, 1912.

Q. 5 Q5; Q6 0 23 6 dweeiaef UNITED STATES PATENT oration.

IQHN JOSEPH RAWLINGS, 0F PU'INEY, LONDON, AND GEORGE SWEETSER, OF UPPER NORWOOD, LONDON, ENGLAND.

nLEc'rmo swrrcn.

Specification of Letters l e/cent.-

Application filed February 25, 1911.

To all whom it may concern:

Be it known that we, JOHN JOSEPH RAW- LINGS and GEORGE Swnncrsnmboth subjects of the King of Great Britain, residing, respectively, at Putney, in the county of London, England, and Upper Norwood, in the county of London, England, have invented certain new and useful Improvements in or Relating to Electric Switches, of which the following is a specification.

This invention has reference to electric switches of the type in which a bow-shaped or buckled spring or the like is acted on by automatically operated devices whlch push it over from one side to the other and in which the quick snap-over action due to the reversal of the curvature of the bow is employed for making or breaking the electric contact.

The invention has reference more particularly to thermal switches having such a snap-over action and in which the automatic pushing movement is obtained by means of a thermostat or expanding element which 1s heated electrically.

A feature of the invention is that the expanding element carries one or more electrical contacts which move therewith and operate the switch with a snap-over action such as referred to.

A further feature of the invention is that the expanding element is itself of a bowshape, and has anelectric heating arrangement consisting of an open-wound coil in a pilot circuit, that is to say a subsidiar circuit, or shunt in which can be inclu ed a removable resistance (such as an incandescent lamp), so that by varying this resistance the switch can be used on circuits of different voltages, without having to interfere with the heater itself. To facilitate the action, the bow-shaped spring contact is carried elastically at its ends by yielding fingers or supports, in order to permit of its elongation as it moves over from one side to the other when its curvature is being reversed.

The invention also comprises other features hereinafter referred to, such as the application of a condenser to switches of this type to reduce the sparking, and a springclip for holding the pusher devices or screw contacts which act on the bow spring.

One use at present contemplated for this improved switch device is as a means for alternatel and automatically switching on two circuits, carrying say from three to five amperes, for lighting two sets of lamps as in advertising apparatus. It may however be applied in any cases in which one or more contacts are to be eriodicall and automatically opened and closed. mi in order that the invention may be clearly understood and readily carried into effect reference will now be had to the accompanying drawings which illustrate one example of the improved switch as arranged to control two branch circuits, and in which Figure 1 is a plan showing the eneral construction of the improved automatlc thermal switch. Fig. 2 is a longitudinal section on the line 2-2 of Fig. 1. Fig. 3 is an underside plan view corresponding to Figs. 1 and 2. Fig. 4 is an enlarged detail view of the automatic contact devices, mainly in section on the line 4% of Fig. 2. Fig. 5 is a detail view hereinafter referred to.

a is the thermostat or expanding element, consisting of a slightly curved or bow-shaped strip of plain brass, this being the metal which we have found to be the most suitable material'for this purpose, as it expands and contracts an indefinite number of times without taking any permanent set or alteration of shape. Mounted on the middle of the strip a, but insulated from it, are two adjustable contact screws I) 6 arranged in line with each other. The ends of the thermostat a are rigidly secured to two blocks or projections c on the base 0 of the switch, which base is made of porcelain, slate or other suitable material.

(Z represents a contact device, such as a bow-shaped spring, which is adapted to snap over from one side to the other, for instance from the full line to the dotted position Fig. 1, and vice versa. This spring isarranged so that its middle point lies between the adjacent but slightly separated ends of the screws 7) b and thus when in the full line position it makes contact with the screw 7), whereas in the dotted position it is in contact with 6 al al are the yielding or elastic fingers which while supporting-the ends of the bowspring 65, permit of its readily assuming a straight form as it passes its mid-position, Whenof course it is elbngated to a certain extent. These fingers al are conveniently all along the element a.

made of spring brass and extend upward from a late 07 screwed under the to of the hollow ass 0 (see Fig. 2). The sai fingers roject upwardly through holes 0 in the base 0 to a sufficient extent to permit the desired yielding motion, and are then bent downward toward each other, the spring (i being carried between the bent down ends. e is a small condenser arranged inside the hollow base 0, and held therein inany convenient way, for instance by a metal stirrup e. the ends of whichpass up through the base and are bent over as at e to form clips.

' In the example shown this condenser is in two parts or halves of which f and f are the extreme terminals, while f is an intermediate terminal connected to the line 9.-

g g are the terminals for the two branches or circuits to be controlled, which for convenience may be termed No. 1 and No. 2

circuits.

It may here be mentioned that the two extreme terminals of the condenser are connected to therespective branch circuit terminals, that is to say fis connected to g, and f to g. The intermediate terminal f of the condenser is connected to the line terminal g ,'as will be seen from Fig. 3.

g is the line terminal by which the current enters or leaves the switch, while is the terminal for the pilot circuit containing the heating coil h which surrounds the thermostat or expanding element a. For the sake of clearness a portion only of this winding is shown diagrammatically in Fig. 2, although it is to be understood that it extends The system of windingthis heating coil it will be more clear from Fig. 5, in which k k are strips of insulating material laid channel-wise along the top and bottom edges of the expanding element a, the wire it being wound over them in open coils, so that a narrow air space exists between each turn and the element 0!. as well as between the turns themselves. Hence the cooling down of the coil h and of the brass strip a is more rapid than 'it would otherwise be, besides which naked will-e can if desired be used for this heating CO1 i The means for mounting the insulated contacts I) b on the element a is of interest and will now be described with reference to Fig. 4. In this figure b b are two brackets which are clamped up to opposite sides of the strip a by means of screws 5*.

The bracket 12 is in direct electrical contact with the thermostatic element a, but suitable insulating slips 6 are arranged as shown, to keep the parts 6 and?) out of electrical communication with each other. The ends bf of each bracket arebent up to form a pair of spring jaws b" which are screw-threaded on their inner sides. Hence they serve as screw sockets, and also grip and hold the corresponding screw 72 or b as the case may be, firmly between them, thus preventing the screw' from shifting after adjustment,'without requiring the use of lock nuts. This Fig. 4 also shows in plan, the turned down ends of the elastic fingers or supports al for holding the contact spring d, and it will be seen that each has a'lateral projection 0Z forming a finger piece by which the jaws can be sprung apart for inserting or removing the contact spring (1, the ends of which are simply slipped into slits or recesses in the adjacent faces of the said turned-down ends.

The arrangement of the connections is as follows: Line terminal 9 is connected to spring contact 03 through its carrier plate (l and is also connected to the middle terminal f of the condenser. The pilot terminal 9 isconnected to the adjacent end of the heating coil k, the other end of which is connected to one end of the brass strip or element a. The terminal 9 of the No. 1 controlled circuit is connected to the terminal f of the condenser and through the element a to the contact screw 6. The terminal g of No. 2 circuit is connected through bracket 6 with contact screw 6 and also to condenser terminal f.

The removable resistance (such as an incandescent lamp) for controlling the heating action of the coil is connected to the pilot terminal 9 and is arranged in series with it outside the switch altogether in any convenient position, it may be at some distance therefrom. This resistance and the coil h are thus in series between a (which receives the potential of the line or main g and the other main of the supply system.

It will be readily understood that if the switch is to be applied to a circuit of say double the voltage to that on which it has been used, it is only necessary to insert a corresponding higher resistance lamp in series with the heating coil h.

Assuming the spring contact at to be in the full-line position shown in Fig. 1, then current can flow from line terminal 9 (through the plate d to said contact a, then to screw contact 6, and (through bracket 1)) to brass expanding element a, and terminal 9 of No. 1 controlled circuit. The half of the condenser corresponding to this position of the spring contactis connected across from line terminal g to and from f to g and is ready to take the spark when the contact a reverses its curve and springs over against screw 6 which it does for the following reasons :The heat-ing coil 71. which is as stated connected to one end of the now live element a and at the other end to the pilot terminal 9 is fully in circuit and is Heating up the said element a. As the temperature of the latter rises therefore, it begins to bulge farther outward and carries with it both screw contacts, and as contact I) is touching the spring a it pushes the latter in front of it, and eventually the said spring snaps over into its dotted line position against contact 12 so putting N0. 2 branch into circuit and cutting out No. l and the heating coil.

The new connections now set up are as follows: From line terminal .9 current flows to plate (Z and spring contact 0? as before, but it now enters the other contact screw, viz. b and. passes thence direct to the terminal 9 leading to No. 2 branch or circuit. The other half of the condenser, connected across from f to g and d, as well as from f to g and Z2 is ready to take the spark when contact is automatically broken between d and 12 .This breaking takes place for-the following'reasons:As the heating coil is at this time out out, the strip or element a will cool and contract, and will slowly flatten its curvature, so pressing the screw 7) forcibly against the spring contact 11 and straightening out the latter until ultimately it passes its middle or dead-center line and once more snaps over against the other contact 6. Thereupon the No. l circuit is again restored, the heating coil h receives current and the strip or element a begins to be re-expanded, these operations continuing automatically as long as the current is supplied from the line.

It will be readily understood that the rate of the alternations, or changes from No. 1 to No. 2 circuit and vice-versa, can be adj usted by means of the screws 1) 6 If these screws be so set that their ends are close together, and that the spring d is forced nearly into its midway or straight position even when the strip or element a is cold, then the apparatus will be very sensitive and the snap over actions will occur at very short intervals, since a slight heating or cooling of the strip a will give sufiicient motion to the screws to throw the spring over to one side or the other. If however the screws be separated more widely, the actions will only occur at longer intervals, as more time will be necessary to bring about the greater changes in the temperature of the strip a which correspond to the greater range of motion required.

What we claim as our invention and desire to secure by Letters Patentis 1. In an automatic electric switch, the combination of a bow-shaped expanding element, a bracket mounted thereon, and carrying an adjustable contact, a second bracket mounted on said expanding element but insulated therefrom and carrying a second contact, a snap-over contact of the buckled spring type arranged between said contacts, and yielding spring-fingers supporting the ends of said spring contact, substantially as described.

2. In an automatic electric switch, the combination of a bow-shaped expanding element, an open-wound heating coil of naked wire mounted on same but insulated therefrom, a bracket mounted on said expanding element and carrying an adjustable contact, a second bracket mounted on said expanding element but insulated therefrom and carrying a second contact, a snap-over contact of the buckled spring type arranged between said contacts, and yielding spring-fingers supporting the ends of said spring contact, substantially as described.

3. In an automatic electric switch, the combination of a bow-shaped expanding element provided with a contact in electrical communication therewith, channel shaped strips of insulating material laid along the top'and bottom edges of said element, a naked heating wire coiled around said eX- panding element and kept apart therefrom by said strips, a second contact mounted on said expanding element but insulated therefrom, a snap-over contact of the buckled spring type arranged between said contacts, and yielding means supporting the ends of said spring contact, substantially as described. v

In testimony whereof we aflix our signatures in presence of two witnesses.

JOHN JOSEPH RAWLINGS. GEORGE SWEETSER. Witnesses:

C. BARNARD BUBDON, B. WESTACOTT. 

